This is a single site, short-term, proof of concept study of riluzole and D-serine for the treatment of tics. Each medication will be evaluated and compared to placebo as part of a double-blind, randomized, parallel, flexible dose, three-arm, 8-week, treatment protocol (D-serine, riluzole, or placebo). A total of sixty patients (age 8-17 years) with TS and moderate to moderately-severe tics will receive study medication according to a 2:1 (dopamine modulating drug: placebo), randomized schedule, i.e., riluzole (n=24), D-serine (n=24), placebo (n=12). The primary outcome measure is tic suppression as determined by changes in the Total Tic Subscore of the Yale Global Tic Severity Scale (YGTSS). Secondary tic outcome measures include changes in the YGTSS Total Score and two Global Impression Scales. Further, since both riluzole and D-serine have been proposed as treatments for obsessive-compulsive behaviors, a TS co-morbidity, these symptoms will be followed. Safety measures include serial physical examinations, vital signs, laboratory studies (comprehensive metabolic panel, complete blood count, plasma amino acids, and urine analyses), documentation of side effects and adverse events, and measurement of changes in ADHD, depression and anxiety.